1. Field of the Invention
This invention relates to an image filing method for compressing image signals, thereby reducing their amount, and recording the compressed image signals on a recording medium, such as an optical disk.
2. Description of the Prior Art
In recent years, image filing systems have been put into practice. With the image filing systems, image signals representing medical images having gradation, or the like are recorded in the form of digital signals on recording media, such as optical disks. When necessary, the recorded image signals are read from the recording media and used in reproduction of visible images on a CRT device, or the like.
In the image filing systems, image signal compression and extension techniques have heretofore been used widely for the purposes of reducing the number of recording media which are stored. With the image signal compression and extension techniques, image signals are compressed and their amount is reduced. Thereafter, the compressed image signals are recorded on recording media. When images are to be reproduced from the image signals, the compressed image signals are read from the recording media and subjected to an image signal extension processing. The image signals thus extended are then used in the reproduction of visible images.
The conventional image filing systems described above utilize optical disks, on which the signals cannot be rewritten, as the recording media. Therefore, the mode in which an image signal is compressed is set when the compressed image signal is originally recorded on an optical disk. After the image signal is compressed in the set mode and the compressed image signal is recorded on an optical disk, the optical disk is kept with the originally compressed image signal stored thereon until the compressed image signal becomes unnecessary.
In general, in cases where an image signal is compressed with a large factor of compression, the image quality of a visible image reproduced from the compressed image signal is very bad. In cases where an image signal is compressed with a small factor of compression, the image quality of a visible image reproduced from the compressed image signal does not become very bad.
Therefore, with the conventional image filing systems described above wherein an image signal compressed with an originally set signal compression processing is kept stored on a recording medium until it becomes unnecessary, the problems described below occurs. Specifically when a signal compression processing is carried out on an image signal with a large factor of compression in order to reduce the number of recording media which are to be stored, the problem occurs in that the image quality of a visible image reproduced from the compressed image signal is very bad. When the image quality of a visible image reproduced from a compressed image signal is to be kept good, the problem occurs in that the factor of compression of the image signal cannot be kept large. Therefore, it is difficult to file image signals efficiently.